1. Field of the Invention
The invention relates to semiconductor process control, and more particularly, to offline measurement for process tool monitoring.
2. Description of the Related Art
Offline measurement measures particles on wafers, thickness of wafers, and abnormal situations for tools using offline measurement tools, adjusting tool statuses and settings for process improvement. Current offline measurement techniques suffer from problems described in the following.
FIG. 1 is schematic view of a conventional system of quality control for semiconductor process tool.
Quality control system 100 comprises data collection unit 110 and constraint system 130. Data collection unit 110 collects process/tool control and analysis data related to semiconductor processes. Conventionally, monitor jobs 111 are defined according to engineering experience and monitor rules, comprising, for example, that tool A is monitored every 12 hours, tool B runs 10,000 pieces of wafers at three-hour intervals, tool C runs 1000 lots a day, and so forth. Monitor data 113 are statistical process control (SPC) data, comprising predefined multiple control charts related to semiconductor processes for management and improvement. Applicable monitor jobs are selected and corresponding monitor data (control charts) is obtained accordingly. Next, the selected monitor data is applied to tools 120, thereby generating monitor results 115. Monitor jobs may be re-defined according to monitor results 115 for process/tool management and control.
Constraint system 130 manages and controls tools 120 according to abnormal states, comprising wafer defects, out of control, and the like. Production loss may be caused by tool monitoring failures. As described, monitor jobs 111 are defined by engineering experience and desired monitor data 113 are obtained accordingly for application to generate monitor results 115. Monitor results 115, however, may be ignored or not immediately provided to constraint system 130 for abnormality management and adjustment, such that abnormal states may still occur again if tools are not adjusted.
Routine tool status monitoring is necessary for good wafer quality control. Such monitor actions can prevent defects found in the Wafer Acceptance Test (WAT) or final test. Routinely performing tool monitor can help to locate potential issues early, not only saving the expense of reworking or scrapping but also reducing the risk of shipping date delays. Currently, an average of 104 monitor rule combinations are applied to each tool. Rules are artificially defined to manage and control the tool quality, such that, when hundreds of monitor rules are applied, monitors may miss a rule resulting in scrapping of a process. With respect to U.S. Pat. No. 6,650,958, integrated process tool monitoring system for semiconductor fabrication, reports are transmitted from process tools directly by uploading parameters to a system for verification, and, if the parameters are incorrect, an alarm is transmitted to terminate the tools.
Currently, monitor tasks are artificially conveyed by order instructions to manage and control the tool quality. The main problem is that the tool quality relies on discipline between engineers and operators, such that invalid lot processing is unpreventable. The U.S. Pat. No. 6,650,958 can only support parameter report directly from process tools.
As described, with respect to current methods for process tool monitoring, production loss may occur when monitor jobs are improperly assigned by experience, monitoring jobs are missed, or monitoring results are ignored. Additional drawbacks of current methods comprise redundant monitor jobs affecting productivity, insufficient monitor jobs affecting production quality, and artificial determination of tool quality.
Thus, an improved method for process tool monitoring is desirable.